Projector

ABSTRACT

A projector includes: a solid-state light source; a diffractive element that dynamically controls diffraction of light from the solid-state light source; a light modulator that modulates, in response to image information, diffracted light emitted from the diffractive element to generate image light; and a projection optical system that projects the image light.

BACKGROUND 1. Technical Field

The present invention relates to a projector.

2. Related Art

In the related art, some projectors include a polarization conversionoptical system that converts the polarization direction of lightincident on a liquid crystal panel to a predetermined direction (e.g.,see JP-A-8-304739).

However, the technique in the related art employs a structure in whichlight is absorbed by a polarizer on the light exiting side of the liquidcrystal panel in black displays thereby failing to effectively uselight. Therefore, it is desired to provide a new technique by which highlight-use efficiency can be obtained.

SUMMARY

An advantage of some aspects of the invention is to provide a projectorcapable of obtaining high light-use efficiency.

According to an aspect of the invention, a projector is provided. Theprojector includes: a solid-state light source; a diffractive elementthat dynamically controls diffraction of light from the solid-statelight source; a light modulator that modulates, in response to imageinformation, diffracted light emitted from the diffractive element togenerate image light; and a projection optical system that projects theimage light.

According to the projector according to the aspect, the light from thesolid-state light source is dynamically redistributed according to adisplay image by the diffractive element, thereby making it possible toeffectively use, as the image light, a component that is absorbed by apolarizer in the related art. Thus, high light-use efficiency can berealized.

In the aspect, it is preferable that the projector further includes acollimating lens that is disposed on an optical path between thesolid-state light source and the diffractive element and collimates thelight from the solid-state light source.

According to this configuration, the light converted to parallel lightby the collimating lens can be incident on the diffractive element. Withthis configuration, the shift of a diffraction image is reduced, andtherefore, a predetermined region of the light modulator can beilluminated by the diffracted light.

In the aspect, it is preferable that the solid-state light sourceincludes a rectangular light emitting region, that a emission angle in along-side direction of the light emitting region is smaller than aemission angle in a short-side direction of the light emitting region,and that the collimating lens includes a first lens surfacecorresponding to the long-side direction of the light emitting regionand a second lens surface corresponding to the short-side direction ofthe light emitting region.

According to this configuration, light emitted from the light emittingregion where the emission angle in the long-side direction is differentfrom that in the short-side direction can be favorably collimated.

In the aspect, it is preferable that a focal length of the first lenssurface is longer than a focal length of the second lens surface.

Further, it is desirable that when a light incident region of thediffractive element is rectangular, the solid-state light source and thediffractive element are disposed such that the short-side direction ofthe light emitting region coincides with a short-side direction of thelight incident region.

According to this configuration, it is possible to cause incident lightto be favorably incident on the diffractive element while reducing thefield angle of the light incident on the diffractive element to 0.03degrees or less. Thus, a predetermined region of the light modulator canbe illuminated with a desired diffraction pattern by reducing the shiftof a diffraction image.

In the aspect, it is preferable that the projector includes a pluralityof the solid-state light sources, and that the plurality of solid-statelight sources are arranged at least along the short-side direction ofthe light emitting region.

According to this configuration, it is possible to improve output ofincident light incident on the diffractive element while reducing thefield angle of the light incident on the diffractive element to 0.03degrees or less.

In the aspect, it is preferable that the plurality of solid-state lightsources are arranged along the short-side direction and the long-sidedirection of the light emitting region, and that the number of thesolid-state light sources arranged in the short-side direction is largerthan the number of the solid-state light sources arranged in thelong-side direction.

According to this configuration, it is possible to further improveoutput of incident light incident on the diffractive element whilereducing the field angle of the light incident on the diffractiveelement.

In the aspect, it is preferable that the diffractive element includes areflective liquid crystal device, and that when the light from thesolid-state light source is obliquely incident on a light incidentregion of the diffractive element, the thickness of a liquid crystallayer of the reflective liquid crystal device is set such that a phasedifference in light passing through the liquid crystal layer duringpower-on and power-off is 2π.

According to this configuration, the diffractive element can adjust thephase difference within the range from 0 to 2π in each diffractionregion also for incident light obliquely incident on the diffractiveelement. With this configuration, the diffraction angle can beaccurately controlled in each diffraction region.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a schematic configuration diagram showing a projector of afirst embodiment.

FIG. 2 is a diagram showing a schematic configuration of an illuminationdevice.

FIG. 3 is a diagram showing the correspondence relationship betweendiffraction regions of a diffractive element and a light modulator.

FIG. 4 is a circuit block diagram showing a circuit configuration of theprojector.

FIG. 5 is an explanatory view of an emission angle distribution of lightemitted from a solid-state light source.

FIG. 6 is a diagram conceptually showing the field angle and beamdiameter of light.

FIG. 7 is a diagram showing a spot formed by a collimating lens of acomparative example.

FIG. 8 is a diagram showing a spot formed by a collimating lens underthe conditions shown in Table 2.

FIG. 9 is a diagram showing a spot formed by a collimating lens underthe conditions shown in Table 3.

FIG. 10 is a diagram showing spots formed by collimating lenses underthe conditions shown in Table 4.

FIG. 11 is a schematic configuration diagram showing an arrangement ofsolid-state light sources according to a modified example.

FIG. 12 is a schematic configuration diagram showing a projector of asecond embodiment.

FIG. 13 is a schematic configuration diagram showing a projector of athird embodiment.

FIG. 14 is a schematic configuration diagram showing a projector of afourth embodiment.

FIG. 15 is an explanatory view of a phase difference occurring whenlight is normally incident on a diffractive element.

FIG. 16 is an explanatory view of a phase difference occurring whenlight is obliquely incident on the diffractive element.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments of the invention will be described in detailwith reference to the drawings.

In the drawings used in the following description, as a matter ofconvenience, a characteristic portion may be shown in an enlarged mannerfor clarity of the characteristic, and thus the dimension ratio and thelike of each component are not always the same as actual ones.

First Embodiment

FIG. 1 is a schematic configuration diagram showing a projector of afirst embodiment.

As shown in FIG. 1, the projector 1 includes a first illumination device2R, a second illumination device 2G, a third illumination device 2B,mirrors 3R and 3B, a light modulator 4R, a light modulator 4G, a lightmodulator 4B, a light combining optical system 5, and a projectionoptical system 6.

The first illumination device 2R emits red light LR. The secondillumination device 2G emits green light LG. The third illuminationdevice 2B emits blue light LB. The mirror 3R reflects the red light LRtoward the light modulator 4R. The mirror 3B reflects the blue light LBtoward the light modulator 4B. The light modulator 4R, the lightmodulator 4G, and the light modulator 4B respectively modulate the redlight LR, the green light LG, and the blue light LB in response to imageinformation to form image lights of the respective colors.

In the embodiment, each of the light modulator 4R, the light modulator4G, and the light modulator 4B includes a liquid crystal panel. Thelight modulator 4R, the light modulator 4G, and the light modulator 4Brespectively modulate the red light LR, the green light LG, and the bluelight LB in response to image information while transmitting the redlight LR, the green light LG, and the blue light LB, and form imagelights corresponding to the respective colors. Polarizers (not shown)are respectively disposed on the light incident and light exiting sidesof each of the light modulator 4R, the light modulator 4G, and the lightmodulator 4B.

A field lens 10R, a field lens 10G, and a field lens 10B thatrespectively collimate the red light LR, the green light LG, and theblue light LB, which are respectively incident on the light modulator4R, the light modulator 4G, and the light modulator 4B, are provided onthe light incident sides of the light modulator 4R, the light modulator4G, and the light modulator 4B.

The light combining optical system 5 includes a cross dichroic prism.The light combining optical system 5 combines the image lights of therespective colors from the light modulator 4R, the light modulator 4G,and the light modulator 4B, and emits the combined image light towardthe projection optical system 6.

The projection optical system 6 includes a projection lens group. Theprojection optical system 6 enlarges and projects the image lightcombined by the light combining optical system 5 onto a screen SCR. Withthis configuration, an enlarged color video (image) is displayed on thescreen SCR.

Subsequently, the configurations of the first illumination device 2R,the second illumination device 2G, and the third illumination device 2Bwill be described. The basic configurations of the first illuminationdevice 2R, the second illumination device 2G, and the third illuminationdevice 2B are the same, except that the colors of illumination lightsare different. In the following, the first illumination device 2R, thesecond illumination device 2G, and the third illumination device 2B arereferred collectively to as “illumination devices 2”, and theconfiguration of the illumination device 2 will be described.

FIG. 2 is a diagram showing a schematic configuration of theillumination device 2.

As shown in FIG. 2, the illumination device 2 includes a solid-statelight source 21, a collimating lens 22, and a diffractive element 23.

In the embodiment, the solid-state light source 21 includes a laserdiode that emits light 1 composed of laser light such as the red lightLR, the green light LG, or the blue light LB. The collimating lens 22converts the light L to parallel light and causes the light L to beincident on the diffractive element 23. The diffractive element 23includes a light incident region (light incident surface) 23 a on whichthe light L is incident. The planar shape of the light incident region23 a is rectangular. In the embodiment, the size of the light incidentregion 23 a of the diffractive element 23 in the short-side direction is4.0 mm, and the size of the light incident region 23 a in the long-sidedirection is 6.4 mm. The diffractive element 23 dynamically controlsdiffraction of the light from the collimating lens 22.

First, the configuration of the diffractive element 23 will bedescribed. The solid-state light source 21 and the collimating lens 22will be described in detail later.

The diffractive element 23 includes a plurality of regions on which thelight L from the collimating lens 22 is incident, and changes thetraveling direction of the light L in each of the regions in response toa control signal. In the embodiment, the diffractive element 23 includesa diffractive optical element (DOE), and, for example, includes a liquidcrystal panel in which liquid crystal molecules are sealed between apair of glass plates through a transparent electrode plate. In thiscase, a diffraction grating using the liquid crystal molecules is formedin each of the regions by applying a voltage through transparentelectrodes in a predetermined pattern.

The number of pixel regions (hereinafter sometimes referred to as“diffraction regions”) set in the diffractive element 23 is the same asthe number of pixels of the liquid crystal panel constituting the lightmodulator 4R, 4G, or 4B. The number of pixel regions of the diffractiveelement 23 is not necessarily the same as the number of pixels of theliquid crystal panel constituting the light modulator 4R, 4G, or 4B, andmay be different therefrom.

When a voltage is not applied to the diffraction region in thediffractive element 23, light transmitted through the diffraction regiongoes straight as it is, and is emitted onto the corresponding pixel ofthe light modulator 4R, 4G, or 4B. On the other hand, when apredetermined voltage is applied to the diffraction region, the lighttransmitted through the diffraction region is diffracted at apredetermined angle by the diffraction region and emitted onto a desiredpixel.

In the embodiment, the diffractive element 23 is configured such thatthe diffraction angle through the diffraction region can be controlledby adjusting the voltage to be applied. The effect of diffraction by thediffractive element 23 efficiently appears as light is in a narrowerwavelength band and has higher directivity. In the embodiment, the lightL emitted from the solid-state light source 21 is laser light, andtherefore, diffracted light can be incident on a predetermined region ofthe light modulator 4R, 4G, or 4B by controlling the voltage to beapplied to each of the diffraction regions in the diffractive element23.

FIG. 3 is a diagram showing the correspondence relationship between thediffraction regions of the diffractive element 23 and the lightmodulator 4R, 4G, or 4B. In FIG. 3, it is assumed that an image patternGP is formed in the image forming region of the light modulator 4R, 4G,or 4B. The image pattern GP includes, for example, a four-by-fourchecker pattern, and includes dark portions GP1 and bright portions GP2.Here, in the related, the dark portion GP1 is formed by absorbing lightwith a polarizer on the light exiting side.

As shown in FIG. 3, the diffractive element 23 controls the voltage tobe applied to the plurality of diffraction regions 24, thereby forming adiffracted light pattern KP corresponding to the image pattern GP formedon the light modulator 4R, 4G, or 4B. The diffracted light pattern KPincludes dark portions KP1 and bright portions KP2. The dark portion KP1corresponds to the dark portion GP1 of the image pattern GP. The brightportion KP2 corresponds to the bright portion GP2 of the image patternGP.

The dark portion KP1 of the diffracted light pattern KP is generated asa result of distributing, through diffraction, light incident on theentire region of the light incident region 23 a of the diffractiveelement 23, to the bright portion KP2. Therefore, the diffractiveelement 23 diffracts light composed of a component (the dark portion GP1of the image pattern GP) that is absorbed by the polarizer on the lightexiting side of the light modulator 4R, 4G, or 4B in the related art,thereby effectively using the light as image light (the bright portionGP2 of the image pattern GP).

FIG. 4 is a circuit block diagram showing a circuit configuration of theprojector 1. As shown in FIG. 4, the projector 1 includes an imagesignal generating unit 7, a panel drive unit 8, a diffractive elementdrive unit 9, and an arithmetic control unit 10. The image signalgenerating unit 7 generates, based on input video signals, signals forthe respective colors to respectively drive the light modulators 4R, 4G,and 4B, and supplies the drive signals to the arithmetic control unit10. The arithmetic control unit 10 supplies the drive signals of therespective colors generated by the image signal generating unit 7 to thepanel drive unit 8.

The panel drive unit 8 drives the light modulators 4R, 4G, and 4B inresponse to the supplied drive signals of the respective colors. Thearithmetic control unit 10 obtains brightness information of pixels froma luminance signal of the input video signals, and calculates adiffracted light pattern (pattern for illuminating pixel regions togenerate image light) formed by the diffractive element 23.

Then, the arithmetic control unit 10 drives the diffractive elementdrive unit 9 so as to form the calculated diffracted light pattern. Thediffractive element drive unit 9 supplies, to the diffractive element23, a control signal for controlling the voltage to be applied to eachof the diffraction regions so as to form a diffracted light pattern forilluminating a predetermined pixel region of the light modulator 4R, 4G,or 4B.

Based on the configuration described above, the illumination device 2 ofthe embodiment dynamically redistributes illumination light according toa display image, thereby being capable of effectively using, as imagelight, the component absorbed by the polarizer in the related art. Thus,light emitted onto dark pixels in the light modulators 4R, 4G, and 4B isdarkened, and also light emitted onto bright pixels is brightened;therefore, a high contrast image can be displayed.

Now, when light control is performed using the diffractive element 23, aproblem arises in that a diffraction image shifts in proportion to thelight incidence angle on the diffractive element 23. When the shift ofthe diffraction image occurs, diffracted light cannot be incident on apredetermined pixel region of the light modulator 4R, 4G, or 4B, therebyfailing to generate a desired image on the light modulator 4R, 4G, or 4Band thus involving the risk of degrading image light.

In contrast, in the embodiment, the light L from the solid-state lightsource 21 is converted to parallel light using the collimating lens 22.With this configuration, the shift of the diffraction image is reducedby reducing the light incidence angle with respect to the diffractiveelement 23.

In general, a light emitting region of the solid-state light source 21is rectangular, and the emission angle distribution varies in thevertical and horizontal directions. That is, the solid-state lightsource 21 has anisotropy in the emission angle distribution. Theemission angle distribution of the solid-state light source 21 will bedescribed below.

FIG. 5 is an explanatory view of the emission angle distribution of thelight L emitted from the solid-state light source 21. In FIG. 5, thecollimating lens 22 is also shown for convenience of description.

As shown in FIG. 5, the solid-state light source 21 includes the lightemitting region 21 a (light exiting surface) to emit light. The lightemitting region 21 a has a substantially rectangular planar shape havinga long-side direction W1 and a short-side direction W2 as viewed in thedirection of a principal ray La of the emitted light.

In the description using FIG. 5, an XYZ coordinate system is used forthe description. In FIG. 5, the X-direction defines the long-sidedirection W1 of the light emitting region 21 a; the Y-direction definesthe direction of the principal ray of the light emitted from the lightemitting region 21 a; and the Z-direction is a direction orthogonal tothe X-direction and the Y-direction, and defines the short-sidedirection W2 of the light emitting region 21 a.

In the embodiment, the width of the light emitting region 21 a in thelong-side direction W1 is, for example, 40 μm, and the width of thelight emitting region 21 a in the snort-side direction W2 is, forexample, 1 μm. However, the shape of the light emitting region 21 a isnot limited to this.

The light L emitted from the solid-state light source 21 is composed oflinearly polarized light having a polarization direction parallel to thelong-side direction W1. The spread of the light L in the short-sidedirection W2 is wider than the spread of the light L in the long-sidedirection W1. In the embodiment, the maximum value (maximum emissionangle) of the spread angle (emission angle) of the light L in thelong-side direction W1 is, for example, 9 degrees, and the maximum value(maximum emission angle) of the spread angle (emission angle) of thelight L in the short-side direction W2 is, for example, 45 degrees. Across-sectional shape BS of the light L is an elliptical shape with theshort-side direction W2 being as a long-axis direction.

That is, the light L has anisotropy in the distribution of emissionangle.

Here, the field angle and beam diameter of the light L incident on thediffractive element 23 can be calculated as follows. FIG. 6 is a diagramconceptually showing the field angle and beam diameter of the light L.In FIG. 6, a corresponds to the half-width of the emission point size(the size of the light emitting region 21 a) of the solid-state lightsource 21; θ corresponds to the field angle (units of degrees (deg)) ofthe light L; W corresponds to the beam diameter of the light L; θ_(L)corresponds to the emission angle (maximum emission angle; units ofdegrees (deg)) of the light L; and f corresponds to the focal length ofa lens surface of the collimating lens 22. The light emitting region 21a has a predetermined size, and therefore, the light emitted from thelight emitting region 21 a is collimated by the collimating lens 22 anddoes not overlap at one point on the light incident region 23 a of thediffractive element 23.

As shown in FIG. 6, the field angle θ can be defined by Equation (1),and the beam diameter r can be defined by Equation (2).θ=a tan(a/f)  Equation (1)r=f·tan θ_(L)  Equation (2)

From Equations (1) and (2), when the focal length f of the collimatinglens 22 is increased, the beam diameter r is increased although thefield angle θ can be reduced, resulting in an increase in product size.

Moreover, the light L emitted from the solid-state light source 21 ofthe embodiment has anisotropy in the distribution of emission angle.

Here, conversion of the light L to parallel light using a collimatinglens having a rotationally symmetric shape about the optical axis willbe described as a comparative example.

Table 1 below shows results of calculation of the field angle θ and thebeam diameter r from Equations (1) and (2), obtained when thecollimating lens (lens having a rotationally symmetric shape) of thecomparative example is used. Table 1 shows calculation results of thefocal length f, the emission angle θ_(L), a beam width R (twice the beamdiameter r), the emission point size a (the size of the light emittingregion 21 a), and the field angle θ in the long-side direction W1 andthe short-side direction W2 of the light emitting region 21 a of thesolid-state light source 21.

TABLE 1 Short-Side Long-Side Direction W2 Direction W1 Focal Length: f4.8 mm 4.8 mm Light Source Emission 45 deg 9 deg Angle: θL BeamDiameter: r 4.0 mm 0.8 mm Emission Point Size: a 1 μm 40 μm Field Angle:θ 0.006 deg 0.24 deg

As shown in Table 1, when the collimating lens 22A having a rotationallysymmetric shape is used, the focal lengths f in the long-side directionW1 and the snort-side direction W2 are both 4.8 mm and equal to eachother. When the collimating lens 22A having a rotationally symmetricshape is used, the beam diameter r and the field angle θ in thelong-side direction W1 are different from those in the short-sidedirection W2.

FIG. 7 is a diagram showing a spot SP formed on the diffractive element23 by the light L transmitted through the collimating lens 22A accordingto the comparative example. In FIG. 7, it is assumed that thesolid-state light source 21 and the diffractive element 23 are disposedsuch that the short-side direction W2 of the light emitting region 21 acoincides with the short-side direction of the light incident region 23a of the diffractive element 23.

As shown in FIG. 7, the spot SP having a substantially elliptical shapewith a length of 4.0 mm in the long-axis direction and a length of 0.8mm in the short-axis direction is formed on the light incident region 23a of the diffractive element 23. Although the size of the spot SP in theshort-side direction of the light incident region 23 a is sufficient,the size of the spot SP in the long-side direction of the light incidentregion 23 a is small. Therefore, the light incident region 23 a cannotbe effectively used.

The present inventor has found that when the field angle θ of the lightL incident on the diffractive element 23 is greater than 0.03 degrees,the above-described shift of the diffraction image remarkably occurs.However, although the field angle θ of the light L is sufficiently small(0.006 degrees) in the short-side direction W2, the field angle θ isvery large (0.24 degrees) in the long-side direction W1.

As described above, when the collimating lens 22A having a rotationallysymmetric shape is used, light use efficiency is low and it is difficultto reduce the shift of the diffraction image.

In contrast, in the embodiment, the collimating lens 22 including afirst lens 25 having a first lens surface 25 a, and a second lens 26having a second lens surface 26 a is used as shown in FIG. 5.

The first lens 25 having the first lens surface 25 a is a surface thatcorresponds to the long-side direction W1 of the light L, functions as acylindrical lens in a plane parallel to the long-side direction W1, andcollimates the light L emitted from the light emitting region 21 a in aplane parallel to the XY plane. That is, the first lens surface 25 aincludes a cylindrical surface having a generating line in the long-sidedirection W1, and collimates the light L spreading in the long-sidedirection W1.

The second lens 26 having the second lens surface 26 a is a surface thatcorresponds to the short-side direction W2 of the light L, functions asa cylindrical lens in a plane parallel to the short-side direction W2,and collimates the light L emitted from the light emitting region 21 ain a plane parallel to the YZ plane. That is, the second lens surface 26a includes a cylindrical surface having a generating line in theshort-side direction W2, and collimates the light L spreading in theshort-side direction W2.

As the collimating lens 22, a collimating lens composed of one lenshaving the first lens surface 25 a on one surface side and having thesecond lens surface 26 a on the other surface side may be used.

Subsequently, conversion of the light L to parallel light using thecollimating lens 22 of the embodiment will be described.

Table 2 and Table 3 below show results of calculation of the field angleθ and the beam diameter r from Equations (1) and (2), obtained when thecollimating lens 22 of the embodiment is used.

Tables 2 and 3 show calculation results of the focal length f, theemission angle θ_(L), the beam width R (twice the beam diameter r), theemission point size a (the size of the light emitting region 21 a), andthe field angle θ in the long-side direction W1 and the short-sidedirection W2 of the light emitting region 21 a of the solid-state lightsource 21.

Under the calculation conditions shown in Table 2, the solid-state lightsource 21 and the diffractive element 23 are disposed such that thelong-side direction W1 of the light emitting region 21 a coincides withthe short-side direction of the light incident region 23 a of thediffractive element 23. On the other hand, under the calculationconditions shown in Table 3, the solid-state light source 21 and thediffractive element 23 are disposed such that the short-side directionW2 of the light emitting region 21 a coincides with the short-sidedirection of the light incident region 23 a of the diffractive element23. That is, there is a 90-degree difference in the arrangement of thesolid-state light source 21 with respect to the diffractive element 23between the conditions shown in Table 2 and the conditions shown inTable 3.

TABLE 2 Short-Side Long-Side Direction W2 Direction W1 Focal Length: f4.8 mm 40.5 mm Light Source Emission 45 deg 9 deg Angle: θ_(L) BeamDiameter: r 4.0 mm 6.4 mm Emission Point Size: a 1 μm 40 μm Field Angle:θ 0.006 deg 0.03 deg

TABLE 3 Short-Side Long-Side Direction W2 Direction W1 Focal Length: f7.7 mm 25.5 mm Light Source Emission 45 deg 9 deg Angle: θ_(L) BeamDiameter: r 6.4 mm 4.0 mm Emission Point Size: a 1 μm 40 μm Field Angle:θ 0.004 deg 0.04 deg

In the collimating lens 22 shown in Table 2, the focal length (25.5 mm)of the first lens surface 25 a corresponding to the light L spreading inthe long-side direction W1 is made longer than the focal length (7.7 mm)of the second lens surface 26 a corresponding to the light L spreadingin the short-side direction W2.

FIG. 8 is a diagram showing a spot SP1 formed on the diffractive element23 by the light L transmitted through the collimating lens 22 shown inTable 2.

As shown in FIG. 8, the spot SP1 having a substantially elliptical shapewith a length of 6.4 mm in the long-axis direction and a length of 4.0mm in the short-axis direction is formed on the diffractive element 23.The spot SP1 is sufficiently large in the long-side direction of thelight incident region 23 a compared to the spot SP of the comparativeexample. Therefore, the entire region of the light incident region 23 acan be used, and thus a desired diffraction pattern can be formed.

Moreover, the field angle θ of the light L can be reduced to as small as0.006 degrees in the short-side direction W2. However, the field angle θof the light L in the long-side direction W1 is 0.04 degrees, which isslightly greater than 0.03 degrees. Therefore, the effect of reducingthe shift of the diffraction image is lowered.

In the collimating lens 22 shown in Table 3, on the other hand, thefocal length (f₁ shown in FIG. 5, 40.5 mm) of the first lens surface 25a corresponding to the light L spreading in the long-side direction W1is made longer than the focal length (f₂ shown in FIG. 5, 4.8 mm) of thesecond lens surface 26 a corresponding to the light L spreading in theshort-side direction W2.

Here, when the emission angle of the light L emitted from thesolid-state light source 21 is large, if the focal length (distancebetween the solid-state light source 21 and a lens) is not reduced, thelens is increased in size by that amount. Therefore, the focal length ofthe lens corresponding to the light having a large emission angle ispreferably reduced. In the embodiment, the focal length f₂ of the secondlens 26 (the second lens surface 26 a) corresponding to the short-sidedirection W2 of the light emitting region 21 a, in which the emissionangle is large and the field angle is small, is reduced; therefore, evenif the focal length is relatively reduced, the field angle is lesslikely to increase. Thus, it is possible to miniaturize the second lens26 without increasing the field angle in the short-side direction W2 ofthe light emitting region 21 a.

Moreover, in order to reduce the field angle in the long-side directionW1 of the light emitting region 21 a to a small value, the focal length(distance between the solid-state light source 21 and a lens) isincreased. In the embodiment, the emission angle in the long-sidedirection W1 of the light emitting region 21 a is small; therefore, evenwhen the focal length of the lens (the first lens 25 having the firstlens surface 25 a) corresponding to the long-side direction W1 isincreased, the first lens 25 is less likely to increase in size. Thus,it is possible to miniaturize the first lens 25 without increasing thefield angle in the long-side direction W1 of the light emitting region21 a.

Hence, according to the embodiment, the lenses 25 and 26 constitutingthe collimating lens 22 can be miniaturized.

FIG. 9 is a diagram showing a spot SP2 formed on the diffractive element23 by the light L transmitted through the collimating lens 22 shown inTable 3.

As shown in FIG. 9, the spot SP2 having a substantially elliptical shapewith a length of 6.4 mm in the long-axis direction and a length of 4.0mm in the short-axis direction is formed on the diffractive element 23.Similarly to the spot SP1, the spot SP2 can use the entire region of thelight incident region 23 a, and thus a desired diffraction pattern canbe formed.

Moreover, the field angles θ of the light L in the short-side directionW2 and the long-side direction W1 are respectively 0.006 degrees and0.03 degrees, which can be both reduced to small values. Thus, as can beseen from Table 3, when the solid-state light source 21 and thediffractive element 23 are disposed such that the short-side directionW2 of the light emitting region 21 a coincides with the short-sidedirection of the light incident region 23 a of the diffractive element23, the shift of the diffraction image can be reduced.

As described above, in the illumination device 2 of the embodiment, thesolid-state light source 21 and the diffractive element 23 are disposedsuch that the short-side direction W2 of the light emitting region 21 acoincides with the short-side direction of the light incident region 23a of the diffractive element 23, so as to satisfy the conditions shownin Table 3.

According to the illumination device 2 of the embodiment, an increase inthe size of the lenses 25 and 26 constituting the collimating lens 22can be suppressed, and also, the light L can be favorably incident onthe entire region of the light incident region 23 a by reducing thefield angle θ of the light L to 0.03 degrees or less. Thus, apredetermined region of the light modulator 4R, 4G, or 4B can beilluminated with a desired diffraction pattern by reducing the shift ofthe diffraction image. Moreover, light absorption by the polarizer isreduced and thus a thermal load is reduced; therefore, the reliabilityof the light modulators 4R, 4G, and 4B can be improved.

According to the projector 1 of the embodiment, a bright image can bedisplayed because the projector 1 includes the illumination device 2 andthus has high light-use efficiency. Moreover, the light emitted ontodark pixels in the light modulators 4R, 4G, and 4B is darkened, and thelight emitted onto bright pixels is brightened; therefore, a highcontrast image can be displayed.

Although the illumination device 2 of the embodiment, which includes onesolid-state light source 21, has been exemplified, the number ofsolid-state light sources 21 is not limited to this. That is, theillumination device 2 may include a plurality of solid-state lightsources 21.

Table 4 below shows results of calculation of the field angle θ and thebeam diameter r from. Equations (1) and (2), obtained when a pluralityof solid-state light sources 21 are used. Under the calculationconditions shown in Table 4, the solid-state light source 21 and thediffractive element 23 are disposed such that the short-side directionW2 of the light emitting region 21 a coincides with the short-sidedirection of the light incident region 23 a of the diffractive element23.

TABLE 4 Short-Side Long-Side Direction W2 Direction W1 Focal Length: f 1mm 40.5 mm Light Source Emission 45 deg 9 deg Angle: θ_(L) BeamDiameter: r 0.8 mm 6.4 mm Emission Point Size: a 1 μm 40 μm Field Angle:θ 0.03 deg 0.03 deg

As shown in Table 4, in order to improve output of the illuminationdevice 2, the focal length of the second lens surface 26 a correspondingto the short-side direction W2 in which the field angle is assufficiently small as 0.006 mm is reduced, and the plurality ofsolid-state light sources 21 are arranged in the short-side directionW2.

For example, the focal length (1 mm) of the second lens surface 26 acorresponding to the light L spreading in the short-side direction W2 isset so as to confine the field angle θ of the light L in the short-sidedirection W2 to 0.03 degrees or less at which the shift of thediffraction image is not affected. In this case, five solid-state lightsources 21 can be disposed in the vertical direction (the Z-directionshown in FIG. 2).

FIG. 10 is a diagram showing spots SP3 formed on the diffractive element23 by the light L transmitted through collimating lenses 22B shown inTable 4.

As shown in FIG. 10, five spots SP3 each having a substantiallyelliptical shape with a length of 6.4 mm in the long-axis direction anda length of 0.8 mm in the short-axis direction are formed on thediffractive element 23. According to the configuration as describedabove, the five spots SP3 are formed on the light incident region 23 a,and thus the entire region of the light incident region 23 a can beeffectively used.

Although the plurality of solid-state light sources 21 arranged in a rowalong the short-side direction W2 have been exemplified in the abovedescription, the solid-state light sources 21 may be arranged along eachof the short-side direction W2 and the long-side direction W1. In thiscase, it is desirable that the number of solid-state light sourcesarranged in the short-side direction W2 is larger than the number ofsolid-state light sources 21 arranged in the long-side direction W1.

For example, in the case of arranging six solid-state light sources 21as shown in FIG. 11, the number of solid-state light sources 21 arrangedin the short-side direction W2 of the light emitting region 21 a is setto three, and the number of solid-state light sources 21 arranged in thelong-side direction W1 of the light emitting region 21 a is set to two.With this configuration, it is possible to improve output of the light Lincident on the light incident region 23 a while reducing the fieldangle of the light L.

Second Embodiment

Subsequently, a projector of a second embodiment will be described.Configurations common to the first embodiment are denoted by the samereference numerals and signs, and a detailed description of theconfigurations is omitted.

FIG. 12 is a schematic configuration diagram showing the projector ofthe second embodiment.

As shown in FIG. 12, the projector 1A of the embodiment includes anillumination device 50, a light separating unit 51, the light modulator4R, the light modulator 4G, the light modulator 4B, the light combiningoptical system 5, and the projection optical system 6.

The illumination device 50 includes a first solid-state light source121R, a second solid-state light source 121G, a third solid-state lightsource 121B, a first collimating lens 122R, a second collimating lens122G, a third collimating lens 122R, dichroic mirrors 52 a and 52 b, amirror 53, and the diffractive element 23.

The basic configurations of the solid-state light sources 121R, 121G,and 121B, and the collimating lenses 122R, 122G, and 122B are the sameas those of the solid-state light source 21 and the collimating lens 22of the first embodiment.

In the embodiment, the first solid-state light source 121R includes alaser diode that emits laser light of red light LR; the secondsolid-state light source 121G includes a laser diode that emits laserlight of green light LG; and the third solid-state light source 121Bincludes a laser diode that emits laser light of blue light LB.

The first collimating lens 122R, the second collimating lens 122G, andthe third collimating lens 122B respectively correspond to the firstsolid-state light source 121R, the second solid-state light source 121G,and the third solid-state light source 121B.

The dichroic mirror 52 a has the optical characteristics of transmittingthe red light LR from the first solid-state light source 121R andreflecting the green light LG from the second solid-state light source121G. The dichroic mirror 52 b has the optical characteristics oftransmitting the red light LR and the green light LG and reflecting theblue light LB from the third solid-state light source 121B. The mirror53 reflects the red light LR, the green light LG, and the blue light LBto cause the red light LR, the green light LG, and the blue light LB tobe incident on the diffractive element 23.

The diffractive element 23 converts the red light LR, the green lightLG, and the blue light LB into a diffraction pattern corresponding to adisplay image of the light modulators 4R, 4G, and 4B similarly to thefirst embodiment.

The light separating unit 51 separates the red light LR, the green lightLG, and the blue light LB converted into the desired diffraction patternby the diffractive element 23, and directs the red light LR, the greenlight LG, and the blue light LB to the light modulators 4R, 4G, and 4B.

The light separating unit 51 includes a first dichroic mirror 60, asecond dichroic mirror 61, and mirrors 62 a, 62 b, 63 a, and 63 b.

The first dichroic mirror 60 reflects the red light LR and transmits thegreen light LG and the blue light LB. The second dichroic mirror 61 isprovided so as to intersect the first dichroic mirror 60, reflects theblue light LB, and transmits the red light LR and the green light LG.

The red light LR reflected by the first dichroic mirror 60 is reflectedby the mirrors 63 a and 63 b sequentially, and is incident on the lightmodulator 4R through the field lens 10R. The blue light LB reflected bythe second dichroic mirror 61 is reflected by the mirrors 62 a and 62 bsequentially, and is incident on the light modulator 4B through thefield lens 10B. The green light LG transmitted through the firstdichroic mirror 60 and the second dichroic mirror 61 is incident on thelight modulator 4G through the field lens 10G.

According to the illumination device 50 of the embodiment, it ispossible to cause the red light LR, the green light LG, and the bluelight LB to be favorably incident on the light incident region 23 a ofthe diffractive element 23 while reducing the field angle. Thus,predetermined regions of the light modulators 4R, 4G, and 4B can beilluminated with a desired diffraction pattern by reducing the shift ofthe diffraction image. Moreover, light absorption by the polarizer isreduced and thus a thermal load is reduced; therefore, the reliabilityof the light modulators 4R, 4G, and 4B can be improved.

Hence, according to the projector 1A of the embodiment, a bright imagecan be displayed because the projector 1A includes the illuminationdevice 50 and thus has high light-use efficiency.

Third Embodiment

Subsequently, a projector of a third embodiment will be described.Configurations common to the second embodiment are denoted by the samereference numerals and signs, and a detailed description of theconfigurations is omitted.

FIG. 13 is a schematic configuration diagram showing the projector ofthe third embodiment.

As shown in FIG. 13, the projector 1B of the embodiment includes theillumination device 50, a field lens 11, a light modulator 4, and theprojection optical system 6.

The third embodiment differs from the second embodiment in that thethird embodiment includes only one light modulator 4. In the embodiment,the first solid-state light source 121R, the second solid-state lightsource 121G, and the third solid-state light source 121B are driven in atime-division manner.

The diffractive element 23 is time-sequentially driven so as to form adiffraction pattern according to incident light (the red light LR, thegreen light LG, or the blue light LB). The light modulator 4 is drivenso as to modulate an image corresponding to the incident light (the redlight LR, the green light LG, or the blue light LB).

According to the projector 1B of the embodiment, the number of lightmodulators can be reduced compared to the configuration of the secondembodiment. Thus, a device configuration becomes simple, and therefore,it is possible to reduce costs and miniaturize the device.

Fourth Embodiment

Subsequently, a projector of a fourth embodiment will be described.Configurations common to the embodiments are denoted by the samereference numerals and signs, and a detailed description of theconfigurations is omitted.

FIG. 14 is a schematic configuration diagram showing the projector ofthe fourth embodiment.

As shown in FIG. 14, the projector 1C of the embodiment includes anillumination device 70, the field lens 11, the light modulator 4, andthe projection optical system 6.

The illumination device 70 of the embodiment includes the firstsolid-state light source 121R emitting the red light LR, the secondsolid-state light source 121G emitting the green light LG, the thirdsolid-state light source 121B emitting the blue light LB, the firstcollimating lens 122R, the second collimating lens 122G, the thirdcollimating lens 122B, the dichroic mirrors 52 a and 52 b, the mirror53, and a diffractive element 123.

The mirror 53 reflects the red light LR, the green light LG, and theblue light LB to cause the red light LR, the green light LG, and theblue light LB to be incident on the diffractive element 123. Thediffractive element 123 of the embodiment includes a liquid crystalpanel including a plurality of pixel regions (diffraction regions) inwhich liquid crystal molecules are sealed between a pair of glass platesthrough pixel electrodes having light reflectivity such as aluminum. Inthis case, a diffraction grating using the liquid crystal molecules isformed in each of the pixel regions by applying a voltage to apredetermined pixel electrode.

That is, the diffractive element 123 of the embodiment differs from thediffractive element 23 of the embodiment described above in that thediffractive element 123 includes a reflective liquid crystal panel(reflective liquid crystal device). The diffractive element 123 actssimilarly to the diffractive element 23, except that the diffractiveelement 123 includes the reflective liquid crystal panel. Therefore, thediffractive element 123 is configured such that a diffraction angle ineach of the diffraction regions can be controlled by adjusting a voltageto be applied.

In the embodiment, similarly to the third embodiment, the firstsolid-state light source 121R, the second solid-state light source 121G,and the third solid-state light source 121B are driven in atime-division manner. The diffractive element 123 is time-sequentiallydriven so as to form a diffraction pattern according to the red lightLR, the green light LG, or the blue light LB (hereinafter sometimesreferred to as “incident light L1”). The light modulator 4 is driven soas to modulate an image corresponding to the incident light L1.

Now, the diffractive element 123 of the embodiment is of a reflectivestructure, and therefore, the incident light L1 needs to be incidentobliquely on a light incident region 123 a.

Here, a phase difference S occurring in light (diffracted light) emittedfrom the diffractive element 123 of a reflective structure can bedefined by S=Δn·2d where d is the thickness (cell gap) of a liquidcrystal layer of the liquid crystal panel constituting the diffractiveelement 123 and Δn is the refractive index difference due to thediffractive element 123.

Here, normal incidence of the incident light L1 on the diffractiveelement 123 will be described. FIG. 15 is a diagram for explaining thephase difference occurring when the incident light L1 is normallyincident on the diffractive element 123. FIG. 15 shows the state ofliquid crystal molecules (index ellipsoids) 130 of the diffractiveelement 123 during power-on and power-off. In FIG. 15, n₀ is an ordinarylight refractive index, and n_(e) is an extraordinary light refractiveindex.

As shown in FIG. 15, the refractive index difference Δn in normalincidence is defined by (n₀−n_(e)). Commonly, (n₀−n_(e)) is set to 2π.That is, the refractive index difference Δn is constant in normalincidence, and therefore, the phase difference in the incident light L1can be easily controlled.

In contrast, in the embodiment, the incident light L1 is incident in anoblique direction on the diffractive element 123. Hereinafter, obliqueincidence of the incident light on the diffractive element 123 will bedescribed.

FIG. 16 is a diagram for explaining the phase difference occurring whenthe incident light L1 is obliquely incident on the diffractive element123. FIG. 16 shows the state of the liquid crystal molecules (indexellipsoids) 130 of the diffractive element 123 during power-on andpower-off. In FIG. 16, n₀(θ) is an ordinary light refractive index, andn_(e)(θ) is an extraordinary light refractive index. In FIG. 16, it isassumed that refraction of light does not occur at the interface betweenthe diffractive element 123 and air for simple description, and theincident angle of the incident light L1 with respect to the diffractiveelement 123 is θ.

As shown in FIG. 16, the refractive index difference Δn in obliqueincidence is defined by (n₀(θ)−n_(e)(θ)). Here, n₀(θ) and n_(e)(θ) areboth defined by the function of the incident angle θ. Therefore, therefractive index difference Δn varies according to the incident angle θand therefore is not constant as in normal incidence, so that a desiredphase difference cannot be obtained.

Thus, the diffractive element 123 cannot illuminate a predeterminedregion of the light modulator 4 with diffracted light, and as a result,a projected image of the projector 1C may be degraded in quality.

In contrast, in the diffractive element 123 of the embodiment, thethickness of the liquid crystal layer is set such that a phasedifference Δnd in light passing through the liquid crystal layer duringpower-on and power-off is 2π. According to this configuration, also forthe incident light L1 obliquely incident on the diffractive element 123,the phase difference can be adjusted within the range from 0 to 2π ineach of the diffraction regions. With this configuration, thediffraction angle can be accurately controlled in each of thediffraction regions.

Hence, according to the illumination device 70 of the embodiment, apredetermined region of the light modulator 4 can be illuminated with adesired diffraction pattern. Thus, light absorption by the polarizer canbe reduced. According to the projector 1C including the illuminationdevice 70, a bright, high-quality image can be displayed because lightuse efficiency is high.

The invention is not limited to the details of the embodiments, and canbe appropriately changed within the scope not departing from the spiritof the invention.

For example, in the embodiments, the liquid crystal panel has beenexemplified as a diffractive element. That is, the phase difference Δndis generated by varying the refractive index difference Δn in each ofthe plurality of diffraction regions, thereby controlling diffraction oflight. It is sufficient that the diffractive element according to theinvention can vary the phase difference, and the diffractive element isnot limited to a liquid crystal panel. For example, diffraction of lightmay be controlled using a diffractive element that generates the phasedifference by varying an optical path length for each of the pluralityof diffraction regions instead of a refractive index.

The entire disclosure of Japanese Patent Application No. 2017-035978,filed Feb. 28, 2017 is expressly incorporated by reference herein.

What is claimed is:
 1. A projector comprising: a solid-state lightsource, wherein the solid-state source includes a rectangular lightemitting region, an emission angle in a long-side direction of the lightemitting region being smaller than an emission angle in a short-sidedirection of the light emitting region; a diffractive element thatdynamically controls diffraction of light from the solid-state lightsource; a collimating lens that is disposed on an optical path betweenthe solid-state light source and the diffractive element and collimatesthe light from the solid-state light source, wherein the collimatinglens includes a first lens surface corresponding to the long-sidedirection of the light emitting region and a second lens surfacecorresponding to the short-side direction of the light emitting region;a driver that selectively applies voltage to the diffractive elementsuch that the diffractive element diffracts the light when the voltageis applied and does not diffract the light when the voltage is notapplied; a light modulator that modulates, in response to imageinformation, diffracted light emitted from the diffractive element togenerate image light; and a projection optical system that projects theimage light, wherein the solid-state light source and the diffractiveelement are disposed such that the short-side direction of the lightemitting region coincides with a short side direction of a lightincident region of the diffractive element, the light incident regionbeing rectangular.
 2. The projector according to claim 1, wherein afocal length of the first lens surface is longer than a focal length ofthe second lens surface.
 3. The projector according to claim 1, whereinthe projector includes a plurality of the solid-state light sources, andthe plurality of solid-state light sources are arranged at least alongthe short-side direction of the light emitting region.
 4. The projectoraccording to claim 3, wherein the plurality of solid-state light sourcesare arranged along the short-side direction and the long-side directionof the light emitting region, and the number of the solid-state lightsources arranged in the short-side direction is larger than the numberof the solid-state light sources arranged in the long-side direction. 5.The projector according to claim 1, wherein the driver controls adiffraction angle of the light through the diffractive element byadjusting the voltage applied to the diffractive element.
 6. Theprojector according to claim 1, wherein the diffractive element includesa plurality of diffraction regions on which the light is incident, andthe driver selectively controls each of the diffractive regions to forma diffracted light pattern.
 7. The projector according to claim 1,wherein a diffraction grating is formed on the diffractive element whenthe voltage is applied, and the diffraction grating is not formed on thediffractive element when the voltage is not applied.